1. Field of the Invention
The present invention relates to differential pressure sensors which require no "fill" fluid and can be constructed in small sizes.
2. Description of the Prior Art
In the prior art types of differential pressure sensors have been advanced, and in connection with vortex flowmeters many differential pressure sensors have been used. However, these sensors generally, are wetted type sensors (thermistors) or the sensor is hermetically sealed in a capsule, the capsule has been filled with a fluid such as an oil. In general, oil filled sensors cannot be used at high or low temperatures because of problems with differential expansion of the fluid vs. sensor components, fluid vaporization, decomposition at high temperatures, high viscosity at low temperatures and other factors. If a wetted sensor fails and has to be repaired the flow line has to be shut down so the entire flowmeter or the sensor capsule can be removed for repair.
Additionally, it has been difficult to obtain accuracy, fast response and low cost in many sensors used with vortex flowmeters. The present device provides a nonwetted (dry) sensor that does not have to be wetted by the fluid being sensed and which is made so it can be serviced without shutting down a flow line when used with a flowmeter. A prior art non-wetted sensor is shown in U.S. Pat. No. 4,005,604. This uses a magnetic dependent member sensing motions of a vibrating member which caused changes in a magnetic field.
A typical prior art differential pressure sensor used with vortex flowmeters is shown in U.S. Pat. No. 3,972,232 and in particular, FIGS. 5-8 thereof. It can be seen that the particular device requires a fill fluid and it cannot be serviced without removing the entire flowmeter from the line with which the flowmeter is used.
A flow measuring device also is shown in U.S. Pat. No. 4,257,277. The device includes pressure sensing devices that open to pressure chambers formed internally in a vortex forming body.
A substantially similar device is shown in U.S. Pat. No. 4,085,614. Also, U.S. Pat. No. 4,088,020 shows a vortex shedding flowmeter with a sensor made to be inserted into the bluff body or bar, which again requires shutting down the line for service of the sensor. However, the device shown in U.S. Pat. No. 4,088,020 is hermetically sealed and permits the bar itself to be formed of cheaper material than the sensor portions.
In general, other differential pressure sensors have utilized bending beam assemblies in larger scale versions, but in the small environment of vortex flowmeters, the problems of obtaining accurate results and still having a low cost and easily assembled sensor become substantial.